If I'm using the video from my GoPro for something like instagram where the quality really only needs to be good enough for a phone then I will use the GoPro Studio software to export the video with the choice for iPhone. (At the moment I'm not sure if it says mobile/iPhone/etc but it should be easy to find once you edit & export).
As far as a full quality video I've used Google Drive before and it worked well although the video could of course take quite a while to upload.
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